In the above noted patent the title compound is prepared by cyclizing N-methyl-N-[2-(2'-chlorophenyl)-ethyl]-2-chloroethylamine hydrochloride under Friedel-Crafts conditions. The cyclization step is carried out using Lewis acids such as aluminum chloride in a melt of ammonium chloride.
U.S. Pat. Nos. 4,251,660 and 4,200,754 disclose a method of preparing tetrahydroisoquinolines. Both of these patents employ aluminum chloride as the cyclization agent. The U.S. Pat. No. 4,251,660 patent teaches that the reaction is done in the absence of an organic solvent. The U.S. Pat. No. 4,200,754 patent discloses that the reaction is done with conventional Friedel Crafts solvents, i.e., methylene chloride, tetrachloroethylene or dichloroethane. Other well known solvents employed during the Friedel Crafts reaction are nitrobenzene or decalin.
The above methods which employ either the conventional solvents or a melt in the process all proved commercially unsatisfactory when used in an attempt to prepare 6-chloro-N-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine. These prior art methods resulted in very poor yields, from relatively no yield to about 25%, with the production of undesired isomers and other impurities.
In addition to the above conventional Friedel-Crafts solvents, chlorinated organic solvents such as monochloro and dichlorobenzene have been attempted with resultant low yields.